An ion implantation apparatus is used for implanting boron ions, phosphorus ions or arsenic ions into wafers of silicon or the like, and usually has an ion source for generating an accelerated ion beam, an electromagnet for mass separation to separate and take out ion beams of particular masses only from the beam of ions, and a slit.
One known technique in this area is to use a rotatably and reciprocally movable disc which holds many wafers disposed in a path of the separated ion beam so that ions are implanted into many wafers at the same time (see U.S Pat. No. 3,778,626).
It has also been known to dispose deflection means between the electromagnet for mass separation and the slit in order to scan the ion beam in the lengthwise direction of the slit so that the ion beam is uniformly implanted onto the wafers (Japanese Patent Laid-Open Nos. 64373/76 and 49774/77).
Recently, it has been proposed to employ doubly charged ions M.sup.++ so that the ions are implanted deeply into the wafers. When the doubly charged ions M.sup.++ are implanted with the conventional ion implantation apparatus, however, the ions M.sup.+ having a different energy level are also implanted into the wafers. That is, ions are not implanted into the wafers in a uniform depth. Moreover, impurities such as neutral particles M.sup.0 may be mixed with the charged ions. In order to preclude this problem, it is necessary to install a large apparatus for deflecting and separating ions between the electromagnet for mass separation and the wafers, which, however, results in very bulky apparatus.